Currently there are several types of semiconductor processing equipment capable of processing silicon wafers at temperatures above 350.degree. C. This type of equipment consists of resistively heated batch furnaces which typically process 25 to 200 wafers per process run. An example of this type of system is the TEL (Tokyo Electron Limited) Alpha 8 vertical furnace. Another system involves a small or mini batch (25-100 wafers) which is also resistively heated but these systems may be used for wafer with a diameter greater than or equal to 300 mm.
There are also single wafer and dual wafer systems which are either resistively heated or lamp heated. An example of the resistively heated system is the Mattson Aspen or the Kokusai Vertron VII resistively heated two-wafer system. An example of the lamp heated system are the Applied Materials Centura RTP/HT or RTP HTF (rapid thermal processing) systems.
An important characteristic of each system is the temperature uniformity and ramp (up and down) capability. If temperature gradient across the wafer is greater than 10.degree. C. at any time, there is a large probability of temperature-induced slip or warpage of the wafer. Table I is a comparison of the temperature ramping capability of present thermal processing tools.
TABLE 1 ______________________________________ Max. Controllable Max. Controllable Number of Temperature Temperature Wafers per Process Tool (ramp up) (ramp down) Batch ______________________________________ Resistively Heated 10.degree. C./min 5.degree. C./min 25-200 (batch furnace) Resistively Heated 100.degree. C./min 60.degree. C./min 25-100 (small batch) Resistively Heated not possible not possible 1 or 2 (single wafer) Lamp Heated 75.degree. C./s 50.degree. C./s 1 ______________________________________
The lamp heated system has the highest ramp rate at greater than or equal to 75.degree. C./s up and greater than or equal to 50.degree. C./s down. The resistively heated single wafer system does not have the capability of controlling the ramp of the wafer temperature. Typically, resistively heated systems, whether a furnace or a single wafer system, are mechanically simpler since the lifetime of the furnace element is five to ten times longer than the lifetime of the lamps. In addition, the use of a thermocouple versus a pyrometery system of temperature measurement favors the resistively heated systems.
With wafer diameters increasing to 300 mm and beyond, single wafer processing is becoming increasingly important because it offers improved process uniformity and reduced defect density.
It is, therefore, an object of the instant invention to provide a wafer processing chamber which is capable of providing a quick temperature ramp up or down.